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  When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are $$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$ $$
  \frac{3}{n(n+1)}$$
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      \begin{align}
      v + w & = 0 &\text{Given} \tag 1\\
      -w & = -w + 0 & \text{additive identity} \tag 2 \\
      -w + 0 & = -w + (v + w) & \text{equations $(1)$ and $(2)$}
      \end{align}
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